There is a secret ingredient behind Sydney's record wet year, and it's not La Niña or climate change.
And for those who know weather, it's not the negative Indian Ocean Dipole (IOD) or the Southern Annular Mode (SAM).
So, if it's not the usual suspects, let's find out the real reason Sydney has suffered through more than 170 days of rain.
La Niña's supporting role
There have been more than 30 La Niña years since 1900, and none have come remotely close to matching 2022 for rainfall in Sydney.
1950 was a strong La Niña — and Sydney's previous wettest year, with a total rainfall of 2,194mm — but we passed that total in early October.
No fingernail-bitting finish to the line, 2022 is the unrivalled, undisputed golden gumboot winner.
While one climate driver in isolation won't break many records, the cards have been heavily stacked against Sydney this year.
All three oceans surrounding our country have been firmly set in a wet phase for Australia's eastern seaboard.
Years similar to 2022 were much drier
Rain during past years, with a wet combination of La Niña, negative IOD and positive SAM was above average, but not record-breaking.
Data for SAM only exists back to 1979, which makes historical comparisons difficult, but for recent decades where we have data — 2021, 2010, 1998, 1989 — all had similar climate drivers to 2022.
The mean rainfall for Sydney during those four years is 1,405mm, nearly 200mm above the long-term mean but more than 1,000mm below what 2022 will reach.
Did climate change increase Sydney's rainfall?
For every 1C increase in temperature, the atmosphere can hold an extra 7 per cent moisture.
It's universally accepted that rising global temperatures are increasing the frequency and intensity of heavy rainfall events, however, averaged over a year this is not sufficient to deliver a record annual total.
The answer is blowing in the wind
It clearly wasn't just the standard climate drivers that caused more rain than has been received since data began in 1859.
The harbour city's weather is highly dependent on the direction of the wind, not unusual for a coastal location. A Southerly Buster is nothing more than a wind change and can drop the temperature 20C in an hour.
Using the US National Oceanic and Atmospheric Administration's (NOAA) Physical Science Laboratory to analyse the wind in Sydney this year, produces a revealing result.
The wind anomaly, or deviation, compared to average has been around 4kph from the east.
It may not sound significant but averaged over an entire year that's a major shift in the prevailing wind.
Other years with a La Niña, negative IOD, positive SAM saw deviations of 0kph (2021), E 1kph (2010), ESE 1.3kph (1998) and SE 1.6 kph (1989).
Quite simply, the wind this year has blown harder from the east, and east of Sydney is a relatively warm Tasman Sea, full of moisture and potential rain.
To illustrate this further, the NSW coast rarely receives heavy rain in a westerly.
1968 was Sydney's driest year since 1900, and no surprise it had a wind deviation of 3 kph from the west.
So while La Niña, negative IOD, positive SAM and climate change all played a role in Sydney's soaking, the answer really is blowing in the wind.
